Transparent optical switching networks are being deployed to direct optical data signals without the need to perform transformation into the electrical domain. In most cases, these switches utilize a beam deflection element to provide the signal redirection, with micro-electro-mechanical-systems (MEMS)-based mirrors being one preferred alternative. Other types of beam deflecting arrangements include planar lightwave circuits (PLCs) which employ Mach Zehnder waveguides and thermal optic switches, digital micro-mirror devices (DMD), or liquid crystals (e.g., liquid crystal on silicon (LCOS)). These switching elements have been used for wavelength-selective switching throughout various communication networks, and are referred to at times as “select and route devices”. Typically these wavelength selective switches are 1×N switches, where N=9, but have been scaled up to 23 ports or higher. Nevertheless, the scale of the switching matrix is inadequate to handle the routing needs of the ever-expanding internet.
To enable a larger switching matrix, M×N wavelength selective switches have been envisioned, but have not been realized due to their complexity. However, new M×N “multicast” optical switches (MSC) have been proposed, which are easier to implement, but usually require amplification to enhance their reach due to the broadcasting nature of the switch. A multicast optical switch is configured such that the input multiplexed signals (or channels) are split into copies and each copy is sent (or “cast”) to several possible detection systems (i.e., broadcasting), where a particular copy and channel to be detected is selected from the multitude of different signals by a switch of some type (e.g., PLC- or MEMS-based switch). In addition, unique output signals or channels from individual transponders or sources are generated and directed by a similar switch to an output combiner, or multiplexed out. Thus, this switching architecture is referred to as a “broadcast and select” routing system.
MCS implemented with PLC technology (e.g., Mach Zehnder interferometers and thermo optic switching) are advantageous since in mass production their cost can be minimized by using batch processing inherent in wafer-based fabrication. The disadvantage of this approach is that the production volumes need to be high to sustain the expensive costs of a fabrication facility, and a new or different M×N MCS switching architecture requires a new set of masks and process runs. Thus, it becomes difficult to pay as you go since PLC it is not a modular approach that can be easily scaled with the increase in switching complexity. PLC MCS also has higher polarization dispersion loss (PDL) than other switching methods, usually higher loss, and other peculiarities (e.g. operational parameters are sensitive to processing parameters used for the wafer and change from batch to batch). Furthermore, the PLC arrayed switch on a section of a wafer is not small and requires a larger hermetic package, heaters, thus more input power and power dissipation schemes. The PLC chip also requires for input and output fiber v-grooves to be aligned and bonded to the chip, further increasing the complexity of the package. As such, packaging is a major cost issue for PLC MCS. Nevertheless, PLCs are widely utilized for low cost 1×N splitters or combiners, but this is a much simpler (and passive) implementation of the technology as compared to MCS.
On the other hand, MEMS-based switches allow a modular pay as you go approach for the construction of an M×N MCS, and may be readily constructed into any M×N configuration. The MEMS switch is relatively simple to package in small hermetic modules (e.g., approximately 7 mm diameter×20 mm long tubes) using only a 1×N fiber array, lens, and MEMS mirror mounted on a header enabling electrical control of the mirror. Of course, MEMS is also a wafer-based fabrication process, but MEMS mirrors are much more ubiquitous than a PLC based MCS and so the volume of MEMS mirrors are leveraged off many different applications. In addition, a 1×N MEMS switch has lower loss and PDL than PLC switches. Nevertheless, for an M×N MEMS-based MCS, the configuration requires the use of a plurality of M 1×N MEMS switches, one for each transmit set of ports and one for each receive set of ports; thus, the cost per switch must be low.
As the switch fabric density continue to increase, it is important that the switches (particularly the MEMS-based switches) operate accurately and efficiently with low loss, high directivity, high isolation and are hitless. In particular, if received optical signals experience a large degree of insertion loss (i.e., low coupling efficiency), they cannot be reliably detected in the presence of noise and other background effects. In many cases, this requires the addition of an amplifier—which increases the cost of the system, an undesirable result. Additionally, as the switch density increases, problems with “cross-talk” also increase, in terms of unwanted signals being coupled into designated signal paths. Thus, improving isolation between multiple signals is also an important goal. Furthermore, the directivity of the coupling must also be high, and the switching event must be hitless. Given the market conditions, it is also important to develop a cost-effective solution that is scalable with the number of connections.